How to preheat the oil pump after maintenance to avoid vacuum formation during operation?

The flow rate of the preheating pump should be low to extend the preheating time.

For specific procedures, refer to the preheating operation guidelines for hot oil pumps; these are available online and on forums.

What I want to say is that many of the technical questions and so-called operating procedures found online do not reflect reality. That’s why it’s posted here for everyone to discuss together

For the pre-heating valve: close the outlet valve, open the pump inlet valve, and use the pump outlet to discharge the sludge line or drain valve in a sealed manner, until hot oil comes out, after which pre-heating can proceed. Open the pump inlet valve, fill the pump, then start it. Directly discharge the oil stored inside the pump into the pump outlet pipeline; after a few seconds, simply stop the pump and proceed with preheating.

It is best to add a cold oil line (three-valve assembly) after the inlet shut-off valve to fill the pump (remember to vent air to ensure that the pump is truly filled). A preheating line should be added after the outlet shut-off valve; during preheating, the cold oil is drained through the three-valve assembly, allowing for gradual heating. This approach ensures that the entire pump as well as the pipes leading to the inlet valve are heated adequately. Once a certain temperature is reached, the drain line of the three-valve assembly is closed, and the inlet valve is opened, thus creating a preheating path from the pump outlet, through the pump, to the inlet. . . I am saying this in relation to the hot oil pump of this device. . (It’s not the technician’s method of operation, because I think there’s something wrong with him.) ）

The reasons for preheating a hot oil pump are as follows: (1) High temperature. The temperature of a hot oil pump is generally around 200–350°C. If it is not preheated, the pump body remains cold; when hot oil enters, the large difference in temperature can cause the pump to be unable to withstand such drastic changes, leading to leaks, cracks, damage to components, and issues arising from the different thermal expansion coefficients of various parts, which may result in them sticking together. (2) High viscosity: The media transported by hot oil pumps have high viscosity; they solidify at normal and low temperatures, and may even seal off the pump’s pipelines, resulting in an inability to start the pump, low flow rates and head pressure, as well as vibrations and noises in the pump. A hot oil pump cannot be used without preheating, but under special circumstances, such as when it is necessary to start it urgently in the event of an accident, the preheating time can be shortened. The preheating method is as follows: (1) The pump intended for hot oil must always be in a hot standby state. That is, oil enters through the preheating pipe at the pump outlet, passes through the pump body, and then exits via the preheating pipe at the inlet to enter the pump’s inlet pipeline and feed the operating pump; when switching pumps, it can be started at any time. (2) If the standby pump is to be overhauled, it does not require preheating; the liquid inside the pump must be drained or emptied, and the pressure must be reduced to zero. After the overhaul, it should be promptly put back into hot standby mode. (3) Cooling water must be supplied to the cooling water jacket of the pump stuffing box (large cover) that is in the preheating stage, to prevent high temperatures from damaging the components or the packing or causing leaks; if necessary, a small amount of seal oil can be applied. (4) To prevent the running pump from being evacuated during the preheating of the standby pump, the outlet valve must be closed, the inlet valve opened, and the drain valve opened to release the air inside the pump before closing it again (someone should monitor this to prevent accidents caused by hot oil leaking out). Then, the outlet valve should be opened 3–4 turns to carry out the preheating process (if a preheating pipe is available, it should be used). (5) During preheating, turn the shaft 180° every 15–20 minutes to prevent bending due to uneven preheating temperatures. Do not use too much oil during preheating to prevent the impeller from rotating in reverse. (6) The pressure in the outlet pipeline of the hot oil pump is greater than the inlet pressure. Therefore, during preheating, the oil in the outlet pipeline can push the oil pressure from the preheating pump back. In this way, it serves as a preheating function. (7) During preheating, if the pump operates to create a vacuum, preheating should be stopped; the vacuum must first be eliminated before preheating can proceed. (8) The preheating temperature should be increased gradually, usually by 50°C per hour; exceptions apply in special cases. Steam can also be used externally around the pump to assist with preheating, thereby increasing and accelerating the preheating rate.

Thank you all for your replies, I’ve learned something